1. Field
The present invention relates generally to power amplifiers of a radio-frequency device. More specifically, the present invention relates to embodiments for a power amplifier including tri-phase digital polar modulator.
2. Background
A wireless communication device (e.g., a cellular phone, a smart phone, a USB modem, a tablet, a communication module, a Bluetooth headset, a wireless LAN radio, etc.) in a wireless communication system may transmit and receive data for two-way communication. The wireless communication device may include a transmitter for data transmission and a receiver for data reception. For data transmission, the transmitter may modulate a radio-frequency (RF) carrier signal with data to obtain a modulated signal, amplify the modulated signal to obtain an output RF signal having the proper output power level, and transmit the output RF signal via an antenna to a base station. For data reception, the receiver may obtain a received RF signal via the antenna and may condition and process the received RF signal to recover data sent by the base station.
The transmitter may include various circuits such as a power amplifier, a filter, etc. Power amplifiers are widely used to provide amplification and output drive for RF signals prior to transmission over the air. For example, power amplifiers are used in Global System for Mobile Communications (GSM) systems, Wideband Code Division Multiple Access (WCDMA) systems, etc. Power amplifiers are also used in base stations as well as in terminals.
When using a digital polar structure for a high efficiency power amplifier, issues with achieving fine resolution values in the in-phase and quadrature (IQ) plane may exist. For example, when there are too few bits of resolution, the signal fidelity suffers degradation, for example through degraded output spectral emissions. Additional challenges in digital polar structures are associated with the mismatch effects caused by practical implementation and layout and their impact on combining efficiency and gain distortion over the range of digital word states. Further additional challenges in polar power amplifiers are encountered due to increasingly stringent delay requirements between amplitude and phase path needed to meet output waveform specifications as the bandwidth of the RF signal increases.